.Hi!
Are you using the embedded sound editor that opens when you click one of “Editor” button above the transport bar – where it says “Tracks, Editor, Mixer, Big Transport” – or are you using the editor that opens up in a new window?
If it’s the first, maybe you minimized it by accident. Try looking for the editor’s title bar:
You can click it and drag it up so the editor becomes visible again.
Otherwise I can’t think of anything right now that could go wrong. I’ve never had something like that happen… 😕
Also, when you say you double-clicked on all four tracks, do you mean you clicked the audio events? Double-clicking the track headers will only bring up the track properties window.
Or…click on an Audio or Midi event first then just click on the Editor button to show the Sound editor…
Edit: Sorry this has been suggested already but enjoy the image it might help… 
